Offshore load handling system

ABSTRACT

A load handling system for offshore load transfer operations, using a floater equipped with a supporting structure for transfer of heavy construction elements between the floater and a transfer site. The supporting structure includes an elongated transfer beam incorporating an arm structure projecting from the floater or a structure attached thereto, and a load carrying point, carried by the arm structure. The load carrying point is displaceable in the longitudinal direction of the arm structure. The arm structure is rotatably supported relative to the floater or a structure attached thereto, in a manner allowing it to be swung in a substantially horizontal plane about a substantially vertical shaft. The arm structure is supported in a manner permitting tilting movements about substantially horizontal axes.

[0001] This application is based on and claims priority under 35 U.S.C. §119 with respect to Swedish Application No. 0103406-5 filed on Oct. 10, 2001, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a system for handling offshore load transfer operations. More particular, the present invention relates to a system for handling offshore transfer operations using a floater device.

BACKGROUND OF THE INVENTION

[0003] The present invention refers to a system for handling offshore load transfer operations, wherein a floater is taken to a transfer site at sea and loads are transferred between the floater and the transfer site. The floater is equipped with a supporting structure carrying the load to be transferred. The floater has adjustable buoyancy for offshore transport, installation and removal of structural elements.

[0004] Such a system is primarily intended for transport, installation and removal of heavy construction elements to or from offshore oil and gas platforms, and uses a floater with load transfer elements protruding from the floater.

[0005] The floater may have any form adapted to or suited for these tasks, and it may, for example, be of the type disclosed in U.S. Pat. No. 6,244,786, which illustrates and describes a column stabilized floater, or a catamaran-like floater, such as disclosed in U.S. Pat. No. 3,078,680. Other suitable floaters are shown in European Patent Publication No. 000 462 A1, French Patent Application No. 247 992, Norwegian Patent Document No. 160424 and Norwegian Patent Document No. 135056.

[0006] The floater is deployed for transportation, installation, or removal of heavy construction elements, to or from fixed structures or floating structures offshore at open sea, hereinafter referred to as “marine structures”. Because the floater may be at open sea, the floater could be exposed to waves.

[0007] The heavy construction element is carried from underneath by beam elements, also referred to as load-transfer beams, which protrude from the floater. The weight of the heavy construction elements is transferred from the floater to the marine structures by ballasting the floater, i.e., filling ballast into ballast tanks of the floater or discharge ballast from the tanks.

[0008] The removal of heavy construction elements from the marine structures from platform topsides or similar structures is a reverse operation to installation. The weight of the heavy construction element is now transferred from a marine structure to the floater by de-ballasting the floater, i.e., removal of ballast from ballast tanks.

[0009] The above described installation and removal techniques have mainly been used for inshore operations in sheltered waters.

[0010] The technique for load-transfer of heavy construction elements to/from marine structures by ballasting/de-ballasting operations, however, introduces relatively large dynamic horizontal loads from the floater acting on the marine structure when performing this operation offshore, in open sea, where the floater is exposed to waves.

[0011] Horizontal dynamic loads pose a serious problem, which could cause damage to the marine structure, especially to old and corroded oil and gas platforms, where topsides have to be removed from platform substructures, known as “jacket” type substructures. Horizontal dynamic loads from the floater can introduce large bending moments at the bottom of the substructure, which is fixed to the seabed. Large shear forces in the substructure as well as large horizontal forces at the contact point between the platform topside and the load carrying point on the load-transfer beams can also occur.

SUMMARY OF THE INVENTION

[0012] In light of this problem, the present invention provides a floater which allows for horizontal motions relative to the marine structure, and especially wave frequency motions during the load-transfer operation.

[0013] The present invention provides an offshore load handling system, which will reduce the horizontal dynamic loads from the floater acting on the marine structure, and which will permit horizontal motions of the floater relative to the marine structure during the load-transfer operation in order to limit horizontal dynamic forces from the floater acting on the marine structure.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0014] The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements.

[0015]FIG. 1 shows schematically one type of a floater used in the load handling system according to the invention.

[0016]FIG. 2 shows schematically and in perspective an outer part of a load transfer beam forming part of the offshore load handling system according to the invention.

[0017]FIG. 3 is a schematic cross section of the load transfer beam shown in FIG. 2.

DETAILED DESCRIPTION

[0018]FIG. 1 shows a perspective view of a floater 20, which in this embodiment has two hulls 21, thereby being of the catamaran type. The floater 20 supports a number of load transfer beams 1, each one supported on a connecting structure 3, which is attached to the floater 20. Preferably, the connecting structures 3 project toward the opposite hull.

[0019] With reference to FIG. 2, the load transfer beam 1 includes a hinged arm 2 connected to the structure 3. In the embodiment shown, the structure 3 is preferably a box girder, which is firmly connected to the floater or forms an integrated part thereof. Preferably, the structure 3 has a forked bracket at its free end. The forked bracket includes two lugs 4, 5 arranged one above the other and substantially parallel to one another. A journalled shaft 6 is arranged to extend substantially vertically between the two lugs 4, 5. The hinged arm 2 is rotatable in the horizontal plane about the journalled shaft 6.

[0020] As can be seen from FIG. 3, the bending moment of the hinged arm 2, at the connection to the structure 3 from the floater, is taken up by two or more radial bearings 7 a, 7 b, and the vertical load is taken by one or more axial bearings 8. The radial bearings 7 a, 7 b could preferably be spherical roller bearings as illustrated and the axial bearing(s) 8 could preferably be a spherical roller thrust bearing. The radial bearings 7 a, 7 b and the axial bearing(s) 8 preferably permit a certain amount of angular misalignment.

[0021] A trolley 9 supports a load carrying point 10. The trolley 9 is designed to move along the hinged arm 2 in a direction from the journalled shaft 6 towards the free end of the hinged arm 2. The trolley 9 is supported on linear bearings 11 (or other bearings with the same feature) on the hinged arm 2.

[0022] In the embodiment shown, the trolley 9 is designed to straddle the arm 2, and the arm 2 is provided with a number of elongated ribs 12 spaced apart in a vertical direction and extending along the vertical sides of the arm 2. These ribs 12 are arranged to cooperate with corresponding ribs or ledgers inside the vertical sidewalls of the trolley 9. The ribs 12 in the arm 2 and the ledgers inside the trolley act as supporting structures for the linear bearings 11.

[0023] The combination of rotation of the arm 2 and linear motions of the trolley 9 allows the load carrying point 10 to operate within an area limited by the rotational angle of the hinged arm and the horizontal stroke of the trolley 9.

[0024] The load carrying point 10 could preferably be a steel plate, supported by a spherical roller thrust bearing 13 or other bearing allowing for rotation about the z-axis and tilt about the x- and y-axes.

[0025] The spherical roller thrust bearing 13 (or other bearing with the same feature) could preferably be supported by a hydraulic jack 14, in order to adjust height of the load carrying points 10 and to control loads on each lifting point 10 when more than one lifting point 10 are working in multiple.

[0026] The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby. 

What is claimed is:
 1. A load handling system for offshore load transfer operations, comprising: a floater equipped with a supporting structure for transfer of heavy construction elements between the floater and a transfer site, the supporting structure including an elongated transfer beam projecting from the floater; a load carrying point connected to the elongated transfer beam, the elongated transfer beam comprising an arm structure, the arm structure at one of its end being rotatably supported relative to the floater or a structure attached to the floater in a manner allowing the arm to be swung in a substantially horizontal plane about a substantially vertical axis; and the arm structure supporting a trolley, the trolley being displaceable in a longitudinal direction of the arm structure and carrying the load carrying point.
 2. The load handling system as claimed in claim 1, wherein the arm structure is arranged about a substantially vertical shaft rotatably supported to an outer end portion of the floater or a structure attached to the floater.
 3. The load handling system as claimed in claim 2, wherein the shaft is supported in at least two bearings accommodating radial loads, and at least one bearing accommodating axial loads.
 4. The load handling system as claimed in claim 3, wherein the bearings accommodating radial loads are spherical roller bearings, and the bearing accommodating axial loads is a spherical roller thrust bearing, both types of bearings permitting angular misalignment.
 5. The load handling system as claimed in claim 1, wherein the trolley is supported in linear bearings provided between the trolley and sidewalls of the arm structure.
 6. The load handling system as claimed in claim 1, wherein the load supporting point supported by the trolley is rotatably supported in a bearing accommodating both axial and radial loads.
 7. The load handling system as claimed in claim 1, wherein the load supporting point is supported on a hydraulic jacket allowing vertical adjustment of the load supporting point.
 8. The load handling system as claimed in claim 1, including means positioned under the load supporting point for allowing tilting movements about substantially horizontal axes.
 9. The load handling system as claimed in claim 1, wherein the arm structure is a girder box having means for guiding the trolley.
 10. A load handling system for offshore load transfer operations, comprising: a floater; connecting structure extending from the floater; an elongated transfer beam supported on the connecting structure and including an arm, the arm being rotatably supported to the connecting structure at an end of the arm so that the arm is rotatable in a substantially horizontal plane; and a trolley supported on the arm, the trolley being displaceable in a longitudinal direction of the arm and carrying a load carrying point.
 11. The load handling system as claimed in claim 10, wherein the arm is arranged about a substantially vertical shaft rotatably supported to the connecting structure.
 12. The load handling system as claimed in claim 11, wherein the shaft is supported in at least two bearings accommodating radial loads, and at least one bearing accommodating axial loads.
 13. The load handling system as claimed in claim 12, wherein the bearings accommodating radial loads are spherical roller bearings, and the bearing accommodating axial loads is a spherical roller thrust bearing, both types of bearings permitting certain angular misalignment.
 14. The load handling system as claimed in claim 10, wherein the trolley is supported in linear bearings provided between the trolley and sidewalls of the arm.
 15. The load handling system as claimed in claim 10, wherein the load supporting point supported by the trolley is rotatably supported in a bearing accommodating both axial and radial loads.
 16. The load handling system as claimed in claim 10, wherein the load supporting point is supported on a hydraulic jacket allowing vertical adjustment of the load supporting point.
 17. The load handling system as claimed in claim 10, including means positioned under the load supporting point for allowing tilting movements about substantially horizontal axes.
 18. The load handling system as claimed in claim 10, wherein the arm is a girder box having means for guiding the trolley.
 19. The load handling system of claim 10, wherein the load carrying point is a steel plate.
 20. A load handling system for offshore load transfer operations, comprising: a floater; at least one elongated transfer beam supported on the floater; an arm rotatably supported on the at least one elongated transfer beam so that the arm is rotatable in a substantially horizontal plane; and a trolley supported on the arm, the trolley being displaceable in a longitudinal direction of the arm and carrying a load carrying point. 